This invention relates to the preparation of silicon nitride containing ceramic materials by the pyrolysis of R.sub.3 SiNH-containing silazane polymers wherein the R.sub.3 SiNH-containing silazane polymers are rendered infusible prior to pyrolysis by treatment with a reactive metal halide. The infusible silazane polymer obtained by treatment with the reactive metal halide has a lower carbon content than the original R.sub.3 SiNH-containing silazane polymer. Upon pyrolysis, the resulting ceramic material has a lower carbon content and relatively more silicon nitride than does the ceramic material obtained by pyrolysis of the original R.sub.3 SiNH-containing silazane polymer. This method is especially suited for the preparation of silicon nitride-containing ceramic fibers.
Ceramic materials have been prepared by the pyrolysis of R.sub.3 SiNH-containing silazane polymers in the prior art. Gaul in U.S. Pat. No. 4,312,970 (issued Jan. 26, 1982), which is hereby incorporated by reference, obtained ceramic materials by the pyrolysis of R.sub.3 SiNH-containing silazane polymers prepared by reacting organochlorosilanes and disilazanes. The R.sub.3 SiNH-containing silazane polymers were pyrolyzed in an inert atmosphere without any separate treatment to render the silazane polymer infusible. Gaul in U.S. Pat. No. 4,340,619 (issued July 20, 1982), which is hereby incorporated by reference, obtained ceramic materials by the pyrolysis of R.sub.3 SiNH-containing silazane polymers prepared by reacting chlorine-containing disilanes and disilazanes. Fibers prepared from such R.sub.3 SiNH-containing silazane polymers were given a "mild heat treatment" in air before pyrolysis but there is no teaching that such a treatment rendered the fibers infusible. Cannady in U.S. patent application Ser. No. 555,755, filed Nov. 28, 1983, which is hereby incorporated by reference, obtained ceramic materials by the pyrolysis of R.sub.3 SiNH-containing silazane polymers prepared by reacting trichlorosilane and disilazane. The R.sub.3 SiNH-containing silazane polymers were not rendered infusible prior to pyrolysis to form ceramic materials.
What has been discovered is a method of rendering the R.sub.3 SiNH-containing silazane polymers infusible prior to pyrolysis thereby producing ceramic materials with decreased carbon levels and increased silicon nitride levels. This method represents a significant advance in the art of preparing ceramic materials, especially in the art of preparing silicon nitride-containing ceramic fibers.